Pruritus and its Association with Cancer and Mortality in Dermatomyositis and Polymyositis: A Nationwide Cohort Study in Taiwan from 2005 to 2022

Background Pruritus is the most common initial symptom reported by patients with dermatomyositis and polymyositis. However, there is limited data regarding the impact of pruritus on cancer and mortality in patients with dermatomyositis and polymyositis. Objective To investigate the associations of pruritus to cancer and mortality in patients with dermatomyositis and polymyositis. Methods This nationwide, population-based retrospective cohort study included adult dermatomyositis and polymyositis patients from Taiwan’s National Health Insurance Research Database between 2005 and 2022. Sex- and age-matched pruritic patients, identified by over six weeks of antipruritic medication use, and nonpruritic patients were analyzed. The primary outcome was cancer occurrence or all-cause mortality. Results Among 919 matched pairs of pruritic and non-pruritic patients, cancer was observed in 19.96% in the long-term pruritic group, 14.63% in the short-term pruritic group, and 10.34% in the nonpruritic group (p<0.0001). All-cause mortality was documented at 30.37% in the long-term pruritic group, 29.69% in the short-term pruritic group, and 37.76% in the nonpruritic group (p<0.0001). Pruritus was associated with an increased risk of cancer (hazard ratio 1.492, 95% confidence interval 1.093-2.036), and a lower risk of all-cause mortality (hazard ratio 0.489, 95% confidence interval 0.419-0.571). Conclusion This population-based study revealed pruritus appeared to be associated with increased cancer risk and decreased all-cause mortality. Thus, pruritus may serve as a pragmatic factor for risk stratification and tailored treatment strategies in dermatomyositis and polymyositis. Comprehensive cancer screening is recommended for patients with dermatomyositis or polymyositis, particularly those presenting with pruritus, whereas patients without pruritus may require vigilant management for potentially life-threatening complications and comorbidities. Key points Previous single-institutional studies and studies with small cohorts reported conflicting data regarding the impact of pruritus on cancer and mortality in patients with dermatomyositis and polymyositis Pruritus in dermatomyositis and polymyositis appeared to be associated with increased cancer risk and decreased all-cause mortality. Our findings suggest that pruritus may serve as a pragmatic factor for risk stratification and tailored treatment strategies in dermatomyositis and polymyositis.